This invention relates to electromagnetic interference (EMI) containment in electronic systems. More particularly, the invention relates to the containment of EMI that is generated in and around an integrated circuit.
Digital electronic systems such as computers tend to radiate electromagnetic energy. Generally this radiated electromagnetic energy is unwanted because it may interfere with the operation of other electronic systems located near the radiating system. This phenomenon is know as electromagnetic interference (xe2x80x9cEMIxe2x80x9d) and radio frequency interference (xe2x80x9cRFIxe2x80x9d). Throughout this document, the term EMI will be used to refer both to EMI and RFI. Government regulations exist in the United States and other countries that specify legal maxima for EMI caused by electronic products. It is therefore important to design electronic products so that the electromagnetic energy generated within them is minimized or effectively contained.
High-speed digital integrated circuit chips such as microprocessors are particularly prominent generators of EMI. Integrated circuit chips of this type also generate a relatively large amount of heat energy, which energy must be removed from the chip or redistributed so that the chip will not overheat and fail.
A need therefore exists for a technique that will help to contain the EMI generated by an integrated circuit chip without impeding the removal of heat from the integrated circuit chip.
In one aspect, the invention includes an EMI containment assembly for an integrated circuit chip. A frame forms an electrically conductive wall around the perimeter of the integrated circuit chip. The bottom of the frame makes an electrically conductive contact with a ground trace on the printed circuit board to which the chip is mounted. The top of the frame makes an electrically conductive contact with an electrically conductive heat removal assembly that is disposed over the top of the chip. An electrically conductive bolster plate is mounted on the side of the printed circuit board opposite the integrated circuit chip and is disposed beneath the chip. Because each component of the assembly is electrically conductive, the assembly creates an EMI cage around the integrated circuit chip. The EMI cage so created is effective to contain EMI generated within the chip. Because the frame does not cover the top of the chip, it does not interfere with the thermally conductive contact that must be made between the top of the chip package and the heat removal assembly. Thus, the assembly of the invention not only provides containment of EMI generated by the integrated circuit chip in a light-weight and cost-effective manner, but it also enables the heat removal assembly to function as effectively as if no EMI containment mechanism were present.